This invention relates to detergent compositions containing polycarboxylates as builders or anti-redeposition agents.
This invention also relates to detergent compositions containing stabilized calcium-sensitive enzymes, wherein the enzymes are not destabilized by the addition of selected builders, including hydrophobically-modified polycarboxylate builders, to the detergent compositions.
The hydrophobically-modified polycarboxylate utilized herein are interpolymers of two or more different ethylenically unsaturated carboxylic acid monomer(s) and one or more ethylenically unsaturated comonomer(s), having a C.sub.8 -C.sub.18 linear or branched alkyl chain ("the polycarboxylates"). In liquid isotropic detergent compositions these builders do not separate into different phases, thus do not require the addition of a compatibilizing agent to the detergent. The polycarboxylates also may be used as anti-redeposition agents in detergents.
The polycarboxylates are prepared by solution polymerization of hydrophobically-modified monomers and carboxylic acid-containing monomers at hydrophobic monomer levels as low as 5 mole percent of the total monomers. The polycarboxylates obtained thereby have a more homogeneous distribution of all monomer units in the polymer chain than those prepared by other processes from identical starting monomers. Better liquid detergent stability, as well as enzyme stability, may be achieved by the use of these homogeneous polycarboxylates.
It is well known that the selection of one copolymerization process over another may affect copolymer qualities as much as, if not more than, other variables, such as monomer selection, monomer ratios and the like. For example, substantially homogeneous acrylate-maleate copolymers have been prepared by controlling the rate of addition of an acrylic monomer to a solution of maleic anhydride in a chain-transfer solvent so as to maintain the monomers and newly formed copolymer in solution. U.S. Pat. No. 4,390,670, issued Jun. 28, 1983, to Walinsky.
Furthermore, copolymers prepared by a single charge, batch process in benzene are not suited for use herein, even though these polymers are derived from comonomers which include an unsaturated carboxylic acid and acrylic esters having aliphatic chain length of 10 to 30 carbon atoms. See, U.S. Pat. No. 3,915,921, issued Oct. 28, 1975 to Schlatzer, Jr. The Schlatzer copolymers are reported to be useful as thickeners for electrolyte-containing materials, including ionic detergents. The Schlatzer copolymers may comprise from 5 to 50 weight percent acrylic ester monomer. The copolymers are insoluble in benzene with the result that the copolymer as recovered by centrifuging the reaction mixture. The copolymer is preferably prepared with an additional, crosslinking monomer so as to provide maximum viscosity.
U.S. Pat. No. 3,940,351, issued Feb. 24, 1976 to Schlatzer, Jr., teaches the preparation of copolymers of an unsaturated copolymerizable carboxylic acid monomer and 10 to 30 carbon atom alkyl acrylate esters in a halogenated solvent (preferably one which is a solvent for the monomers but not for the polymer) by a single charge batch process wherein the polymer is recovered by centrifuging the reaction mixture. Maximum polymer viscosity in electrolyte-containing aqueous media is an object of the patent, and optional crosslinking monomers are preferably employed to achieve this object. Although Schlatzer discloses the use of these polymers as thickeners in ionic detergents, the Schlatzer polymers are not suited for use herein, being compositionally and functionally distinct from the polymers prepared by the process disclosed herein. The Schlatzer polymers are designed to thicken, whereas the polymers herein advantageously contribute little to the viscosity of isotropic liquid detergents.
Detergent compositions are generally a blend of a surfactant(s), builder(s) and, optionally, ion exchanger(s), filler(s), alkali(es), anticorrosion material(s), anti-redeposition material(s), bleach(es), enzyme(s), buffer(s), optical brightener(s), fragrance(s), solvent(s) and other components selected for particular applications.
Builders are used to improve the effectiveness of detergent compositions and thereby improve their cleaning powers. The manner in which detergent builders improve the cleaning powers of detergent compositions is related to a combination of factors such as emulsification of soil particles, solubilization of water insoluble materials, promoting soil suspension in the wash water so as to retard soil redeposition, sequestering of metallic ions, and the like. Builders enhance (or "build") the cleaning efficiency of surfactants by forming complexes with hard water ions, aiding in keeping soil from redepositing on fabric being washed and buffering or moderating the pH of wash water.
Many materials are or have been used as builders in detergent formulations. None of the high capacity calcium-binding builders have been recommended for use in the presence of calcium-sensitive enzymes in liquid detergent formulations. As heavy duty liquid laundry detergents gain market share, there is a particular need for effective builders which are compatible with liquid detergents and do not detract from enzyme stability.
At a minimum, detergent builders for liquid isotropic detergents must be effective calcium binders, compatible with the liquid formulations and shelf-stable. Builders which precipitate from the liquid, or cloud or gel the liquid, or cause phase separation or solid settlement initially or upon storage, are not suitable for use in liquid detergents unless an effective compatibilizing agent can be found. Structured liquids and powdered detergent formulations, which have less demanding requirements for builder compatibility and stability, can employ a greater variety of builders without an added compatibilizing agent.
Citric acid and its salts are used commercially as builders in liquid detergent formulations. While very compatible in liquids and free of known adverse effects on enzyme stability, the citrates do not bind calcium nearly as effectively as the builders used in powdered detergents.
Also used commercially are the liquid detergent builders comprising ether carboxylate salts (i.e., tartrate monosuccinate and disuccinate salts) which are disclosed in U.S. Pat. No. 4,663,071, issued May 5, 1987 to Bush, et al. Among the polymeric materials that have been suggested for use as liquid detergent builders are polymeric polycarboxylic acids. U.S. Pat. No. 4,797,223, which issued Jan. 10, 1989 to Amick, et al., discloses water soluble polymers with surfactant radicals distributed along a carboxylated polymer chain. The polymer may contain surfactant end groups. The surfactant radical is selected from a group of radicals having poly(alkyleneoxy) blocks characterized by a hydrophobic portion and a hydrophilic portion.
U.S. Pat. No. 4,612,352 which issued Sep. 16, 1986 to Schafer, et al., discloses water soluble or water dispersible graft polymers having at least 10 percent, by weight, of a hydrophilic graft constituent bonded to carbon and at least one hydrophobic radical bonded to the graft constituent by a polyglycol ether chain. These graft polymers contain pendant surfactant-type groups.
U.S. Pat. No. 4,559,159, which issued Dec. 17, 1985 to Denzinger, et al., discloses polymers of ethylenically unsaturated mono- and di-carboxylic acids, together with not more than 15 percent, by weight, of carboxyl-free monomers, having a terminal hydroxy radical and one or more alkylene oxide radicals.
Unlike the polycarboxylates disclosed herein, which comprise the polymerized residue of hydrophobic alkyl ester monomers and hydrophilic carboxylic acid monomers, and are polymers having overall surfactant character, each of these builder compositions acquire liquid detergent formulation compatibility through the presence of pendant surfactant-type radicals on the carboxylated polymer chain. It is unexpected that liquid detergent compatibility may be achieved without employing surfactant radicals in the polymer.
It is even more unexpected that these builders do not destabilize calcium-sensitive enzymes in liquid detergent formulations, yet provide builder efficacy equivalent to that of builders used commercially in powdered detergents.
The desirability of using enzymes in cleaning compositions is well known. Protease enzymes, for example, are useful for their ability to reduce proteinaceous stain which then can be readily washed away. Proteases are calcium-sensitive enzymes which denature when calcium is removed from calcium binding sites on the enzyme. See, Novo's Handbook of Practical Biotechnology, C. O. L. Boyce, Ed., Novo Industri A/S, 1986, pp. 54-57; and U.S. Pat. No. 4,318,818, issued Mar. 9, 1982, to Letton, et al.
The stability of enzymes, e.g., lipases and proteases, in commercial liquid detergent compositions is generally poor due to various reasons. Builders which strongly bind calcium may strip the calcium from calcium-sensitive enzymes, causing loss of enzyme activity, initially, during storage of detergent compositions, or during use. The surfactant found in such detergent compositions may induce denaturation of the enzyme. When a protease is present in the composition, the protease can cause proteolytic digestion of other enzymes, or of itself in a process called autolysis.
Proteins, such as those taught in U.S. Pat. No. 4,842,758 to Crutzen and U.S. Pat. No. 4,842,767 to Warschewski, et al., are known to improve enzyme stability in heavy duty liquid detergents (HDLs).
Other approaches used for stabilization of enzymes in HDLs include the use of aminated polysaccharides such as taught in U.S. Pat. No. 4,011,169; the use of calcium and carboxylic acids (preferably formate) such as disclosed in U.S. Pat. Nos. 4,305,837, 4,490,285 and 4,537,707; the use of calcium with alkyl diacids (succinic, adipic) such as disclosed in U.S. Pat. No. 4,529,525; and the use of aliphatic glycols with and without boron containing compounds such as taught in U.S. Pat. Nos. 3,819,528, 4,462,922, 4,404,115 and 4,652,394.
West German published patent application No. P 29 37 012.5 teaches agents for stabilizing enzymes which are the protein reaction products of protein substrates and (1) ammonia or primary or secondary amines containing up to 20 carbon atoms and/or (2) aliphatic epoxides containing 2 to 18 carbon atoms. Proteins used as substrates for addition of these groups include gelatin, collagen, zein, casein, soy protein and other plant proteins as well as so-called single-cell proteins. Gelatin, collagen or casein are said to be preferred.
The use of selected builders to avoid destabilizing calcium-sensitive enzymes in detergent compositions has not been previously disclosed. It has been found that selection of a builder having a pKCa (i.e., the intrinsic calcium binding constant, as determined by the method of Example 5, herein) of at least 5.0 in a low ionic strength system (e.g., about 20 mmols/liter monovalent ion) and having a pKCa of less than 3.5 in a high ionic strength system (e.g., about 400 mmols/liter monovalent ion) will permit formulation of a detergent composition containing highly effective builders and enzymes, particularly proteases. Preferred builders include the polycarboxylates described herein. The pKCa is calculated as set forth in Example 5, herein.